RSSArchive for February, 2011

Designing capsules for space

WHY WAS THE APOLLO capsule shaped like a gumdrop? Learn about the blunt-shaped capsules used for past and present NASA spacecraft in this NASA video, which shows how engineers come up with novel and useful designs.

Adapted from information issued by NASA.

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What’s up? Night sky for March 2011

Silhouette of people with telescopes

Saturn and Venus will be the planets to watch for when you're out stargazing in March 2011.

THIS MONTH, Venus will be visible in the eastern morning sky for quite some hours before sunrise. You won’t be able to miss it—it will be big and bright and wonderful.

Mercury will be very low down on the western horizon after sunset this month, and will be very difficult to see.

Mars has been lost in the glare of the Sun since early February, but during March will begin to make its reappearance in the eastern morning sky. It will be too low to be seen until towards the end of the month, however, at which time it will rise about an hour before the Sun.

Jupiter is about to be lost in the glare of the Sun. It is very low down in the west after sunset, and by the end of the month it will set (ie. drop below the horizon) only 15 minutes after the Sun does, making it essentially impossible to spot.

Saturn is the evening planet to see at the moment, rising roughly two hours before midnight and riding high in the northern sky throughout the night.

Except where indicated, all of the phenomena described here can be seen with just the unaided eye. And unless otherwise specified, dates and times shown here are for the Australian Eastern Daylight Time zone, and sky directions are from the point of view of an observer in the Southern Hemisphere.

March 1

Look for the crescent Moon above and to the left of Venus in the eastern morning sky. Also, if you’re out stargazing after 10:00pm, look to the northeastern sky and you’ll see two fairly bright stars side by side. The one on the right is Spica, the brightest star in the constellation Virgo. The one on the left is actually a planet, Saturn.

Silhouette of people and telescopes

Autumn nights are good for stargazing.

March 5

New Moon occurs today at 7:46am Sydney time (March 4, 20:46 Universal Time).

March 6

Today the Moon will be at the farthest point in its orbit, called apogee, at a distance from Earth of 406,584 kilometres.

March 13

It is First Quarter Moon today at 10:45am Sydney time (March 12, 23:45 Universal Time).

March 17

The almost-full Moon will be above and to the left of Regulus, the brightest star in the constellation Leo.

March 18

In a demonstration of how it’s position changes from one night to the next, tonight the Moon will be above and to the right of Regulus.

March 20

Full Moon occurs today at 5:10am Sydney time (March 19, 18:10 Universal Time). Today also marks the Moon’s perigee, which is the opposite of apogee, ie. the point in its orbit when it is closest to the Earth. The distance between the two bodies today will be 356,578 kilometres. Apogee and perigee distances are not exactly the same from month to month, and it turns out that this month’s lunar perigee will be the closest for all of 2011.

Finally, have a look just below and to the right of the Moon and you’ll see a brightish ‘star’ with a yellow tinge—this is actually the ringed planet Saturn. If you have a telescope, or know someone who does, turn it to Saturn and marvel at the sight of its majestic rings.

People stargazing at night

All the sights described in the text can be seen with the unaided eye.

March 21

Today marks the equinox, when the Sun heads north of the equator. It is the point midway between the midpoint of summer and the midpoint of winter for those in the Southern Hemisphere.

Also, have a look just below and to the left of the Moon, and you’ll see a fairly bright star. This is Spica, the brightest star in the constellation Virgo.

March 25

The Moon will be above and to the right of red Antares, the brightest star in the constellation Scorpius.

March 26

It is Last Quarter Moon today at 11:07pm Sydney time (March 26, 12:07 Universal Time).

March 31

Look for the crescent Moon above and to the left of Venus in the eastern morning sky.

If you have any questions or comments on the night sky, we’d be happy to answer them. Please use the feedback form below. Happy stargazing!

Images courtesy IAU.

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Black hole destroys its own ‘dinner’

Artist’s illustration of the outflow in the heart of galaxy Markarian 231

Artist’s illustration of the outflow in the heart of galaxy Markarian 231, produced by a black hole.

A VORACIOUSLY FEEDING black hole creates a ‘wind’ that pushes its own ‘food’ of dust and gas out of reach, astronomers using the Gemini North telescope in Hawai’i have found.

They think this is the process that turned actively feeding black holes—common in the early universe—into the quiescent ones found in galaxies today.

“It looks like they’ve found the ‘off switch’ for black holes,” said Professor Joss Bland-Hawthorn of the University of Sydney, who studies galactic winds.

“We’ve long suspected that a negative feedback process like this must be at work, but these Gemini observations are the first clear evidence of outflows that can starve a black hole of fuel.”

The research will be published in the Astrophysical Journal on 10 March.

Galaxy Markarian 231

The galaxy Markarian 231 contains a massive black hole that is pushing gas and dust away from itself. Hubble Space Telescope image.

Astronomers Professor Sylvain Veilleux (University of Maryland, USA) and Dr David Rupke (Rhodes College, Tennessee, USA) studied the galaxy Markarian 231, which lies 600 million light-years away.

Markarian 231 is a ‘train wreck’ resulting from the collision of two galaxies. At its centre is a black hole at least ten million times the mass of the Sun, which is sucking in gas and dust from its immediate surroundings.

Galactic centre boiling over

The black hole in Markarian 231 was known to produce narrow outflows (‘jets’) but the Gemini observations have revealed a broad outflow extending in all directions for at least 8,000 light-years around the galaxy’s core.

More than one physical process is likely to be creating the outflow. One is thought to be the X-rays and gamma rays generated around the black hole, which heat up the gas in the galaxy’s centre until it ‘boils over’.

Gas is streaming away from the galaxy’s centre at speeds of over 1,000 kilometres a second—fast enough to travel from Sydney to Perth in four seconds. The flow is sweeping away huge amounts of gas.

“The fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow,” Rupke said.

As extreme as Markarian 231 appears, Veilleux says that it is probably not unique. In the early universe galaxies like this “are seen in large numbers and all of them may have gone through shedding events like the one we are witnessing in Markarian 231,” he said.

Australia has a 6.2% share of the international Gemini partnership. Australian astronomers’ access to the Gemini telescopes is managed through the Australian Gemini Office, hosted by the Australian Astronomical Observatory (AAO), Australia’s national optical observatory. The AAO is part of the Commonwealth Department of Innovation, Industry, Science and Research.

Adapted from information issued by AAO. Markarian 231 courtesy NASA / ESA / Hubble Heritage Team / A. Evans. Illustration courtesy Gemini Observatory / AURA / Lynette Cook. Gemini telescope image courtesy Gemini Observatory.

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ATV docks with Space Station

The European Space Agency’s Johannes Kepler Automated Transfer Vehicle, or space cargo ship, has docked with the International Space Station … as seen in the video footage above.

The video below explains the launch and purpose of the ATV.

Videos courtesy ESA.

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Leaders praise Aus-NZ SKA bid

PRIME MINISTERS Julia Gillard and John Key praised the joint SKA bid during recent talks in New Zealand.

The Prime Ministers reaffirmed their countries’ strong ties during recent talks in New Zealand, where they met to sign a trade agreement to promote closer economic relations between the two countries.

During the talks, Prime Ministers Key and Gillard praised the Australian and New Zealand SKA (anzSKA) bid to host the SKA which is seen as a good example of strong trans-Tasman economic and social ties.

Map of potential SKA stations in Australia and New Zealand

If Australia and New Zealand win the bid to host the Square Kilometre Array, antennae will be spread across the two countries.

“Our joint determination to bring the multibillion-dollar Square Kilometre Array radio-telescope project to this part of the world is a great example of how working together strengthens our position internationally,” The Prime Ministers wrote.

The comments have bolstered Australian and New Zealand astronomers who are already working closely together after the successful link up of six radio telescopes across the Tasman Sea.

The linked telescopes will make images ten times more detailed than those of the Hubble Space Telescope and has already been used to generate unparalleled images of nearby galaxy Centaurus A.

Adapted from information issued by www.ska.gov.au. Image courtesy CSIRO. Video courtesy www.skatelescope.org

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Is gravity wrong?

NGC 1300

Comparison of galaxies' mass estimates and their spin rates pose challenges for the standard theory of gravity. A newer theory called MOND aims to solve the riddle.

A STUDY OF THE SPIN RATES of gas-rich galaxies supports an alternate theory of gravity known as MOND, according to work by University of Maryland Astronomy Professor Stacy McGaugh.

This latest of several successful MOND predictions, raises new questions about the accuracy of the reigning cosmological model of the universe, writes McGaugh in a paper to be published in March in the journal Physical Review Letters.

Modern cosmology says that for the universe to behave as it does, the mass-energy balance of the universe must be dominated by dark matter and dark energy. However, direct evidence for the existence of these invisible components remains lacking.

An alternate, though unpopular, possibility is that the current theory of gravity does not adequately describe the dynamics of cosmic systems.

Enter MOND

A few concepts that would modify our understanding of gravity have been proposed. One of these is Modified Newtonian Dynamics (MOND), which was hypothesised in 1983 by Moti Milgrom, a physicist at the Weizmann Institute of Science in Rehovot, Israel.

One of MOND’s predictions specifies the relationship between the overall mass of a galaxy and its rotation velocity. However, uncertainties in estimating the masses of star-dominated spiral galaxies (such as our own Milky Way) previously had prevented a definitive test.

Galaxies UGC 2885 and F549-1

The star-dominated spiral galaxy UGC 2885 (left) and the gas-rich galaxy F549-1 (right). A new study of the spin rates of gas-rich galaxies supports an alternate theory of gravity. Images by Zagursky and McGaugh.

To overcome this problem, McGaugh instead examined gas-rich galaxies, which have fewer stars and a lot more mass in the form of interstellar gas. He says it is easier to gauge the mass of gas than of stars.

McGaugh compiled a sample of 47 gas-rich galaxies and compared each one’s mass and rotation velocity with the relationship expected by MOND.

All 47 galaxies fell on or very close to the MOND prediction.

By comparison, no dark matter model performed as well.

MOND vs the rest

Almost everyone agrees that on scales of large galaxy clusters and up, the Universe is well described by the dark matter-dark energy theory. However, according to McGaugh, it does not account well for what happens at the scales of individual galaxies and smaller.

“MOND is just the opposite,” he said. “It accounts well for the ‘small’ scale of individual galaxies, but MOND doesn’t tell you much about the larger universe.”

“If we’re right about dark matter, why does MOND work at all?” asks McGaugh. “Ultimately, the correct theory—be it dark matter or a modification of gravity—needs to explain this.”

Adapted from information issued by University of Maryland. Galaxy image courtesy NASA / ESA / HHT / STScI / AURA / Hubble Collaboration.

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Amateur astronomy milestone

Illustration of stargazers

Thousands of amateur astronomers monitor interesting stars throughout the year. Professional astronomers make good use of the data collected.

  • Amateur astronomers monitor brightness changes of “variable stars”
  • Brightness changes reflect physical changes happening within the stars
  • Professional astronomers rely on amateur observations

A CITIZEN SCIENCE PROJECT running for over 100 years reached a key milestone this month when an amateur astronomer contributed the 20 millionth observation of a variable star on February 19, 2011.

A variable star changes in brightness over time. Records of these changes can be used to uncover the astrophysical processes within evolving star systems.

With a database going back over a century, variable star astronomers have access to a data source unparalleled in astronomy.

“The long-term study of stellar brightness variation is critical to understanding how stars work and the impact they have on their surroundings,” said Dr Kevin Marvel, Executive Officer of the American Astronomical Society. “The noble efforts of the engaged AAVSO volunteers play an important role in astronomy and help expand human knowledge.”

Amateur astronomers have been recording changes in the brightness of stars for centuries. The world’s largest database is run by the American Association of Variable Star Observers (AAVSO) and was started in 1911, making it one of the oldest continuously operating citizen science projects in the world.

Hubble image of stars

Variable stars are ones that change their brightness periodically or spasmodically. Astronomers want to know why.

“Because some variable stars are unpredictable and/or change their brightness over long time scales, it is not practical for professional astronomers to watch them every night. Thus, amateurs were recruited to keep tabs on these stars on behalf of professionals,” Dr Arne Henden, Director of the AAVSO, said.

20 million and counting

The 20 millionth observation was made by Dr Franz-Josef “Josch” Hambsch of Belgium. The observation was of GV Andromeda, which is in a class of older, pulsating stars smaller than our Sun.

I like these stars because you can see their entire variation cycle in one night. There have not been many recent observations made of this particular star, so that is why I am monitoring it,” Hambsch said. Hambsch is also a member of the Belgium variable star organisation, Werkgroep voor veranderlijke sterren (WVS).

The AAVSO currently receives variable star brightness estimates from about 1,000 amateur astronomers per year. Special equipment is not necessarily needed. While some variable stars require high-tech equipment, others are bright enough to be seen with the unaided eye.

Also, the AAVSO has a network of six robotic telescopes that are available to members free of charge.

Invaluable contribution by amateurs

Making an estimate of a variable star’s brightness can be a time-intensive procedure and requires careful training. The observer must identify the star in the sky and then compare its brightness with those of other, nearby stars that are steadfast in their own brightness.

The process can range from less than a minute to many hours per estimate, but typically takes about five minutes. At that rate, observers have invested the equivalent of about 1.7 million hours of time in collecting observations for the database.

Assuming a current median salary of US$33,000, this would be the rough equivalent of US$27.5 million worth of donated time if all the observations were reported today.

“The reality is these observations are invaluable. The database spans many generations and includes data that cannot be reproduced elsewhere. If an astronomer wants to know the history of a particular star, they come to the AAVSO,” Henden said.

More information:

AAVSO

Variable Star Section, Royal Astronomical Society of New Zealand

Adapted from information issued by AAVSO. Illustration courtesy Nico Camargo and AAVSO. Star image courtesy NASA / ESA / Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain).

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Discovery’s final flight

NASA IS ABOUT TO LAUNCH space shuttle Discovery on its final voyage into space. The STS-133 mission will take extra equipment and spare parts to the International Space Station.

Lift-off is due at 8:50am Sydney time on Friday, February 25 (4:50pm US EST on Thursday, February 24).

The video above is a 10-minute-long NASA production that describes Discovery’s history and covers the STS-133 flight. Note that this video was produced in October 2010, before the original launch date of November 2010. Launch was delayed until this month due to a problem with the external fuel tank. Also, there has been one substitution in the crew.

The video below is a 24-minute-long NASA briefing that explains what the astronauts will be doing during the mission, and includes amazing computer-generated graphics.

Adapted from information issued by NASA.

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‘Weird science’ of neutron stars

Cassiopeia A and an artist's impression of a neutron star

Nebula Cassiopeia A, the remains of a massive star that exploded as a supernova. At it's heart is a neutron star (inset, artist's impression), where densities increase from the crust (orange) to the core (red) and finally to the core region where a "superfluid" exists (inner red section).

ASTRONOMERS HAVE GLIMPSED the inner workings of a neutron star and found a unique world where the physics can only be described as “weird.”

A neutron star is the extremely dense, collapsed core left behind from an exploding star, or supernova.

University of Alberta astronomer Craig Heinke’s team found that the neutron star’s core contains a superfluid … a friction-less liquid that could seemingly defy the laws of gravity.

“If you could put some of this superfluid in a jar it would flow up the walls of the container and over the edge,” said Heinke.

Heinke says the core of the neutron star also contains a superconductor, a perfect electrical conductor.

“An electric current in a superconductor never loses energy—it could keep circulating forever.”

Neutron stars contain the densest known matter that is directly observable. One teaspoon of neutron star material weighs six billion tonnes.

“Depending on their composition, superconductors created in laboratories on Earth stop working at anything warmer than -100 to -200 degrees Celsius,” says team member Wynn Ho of the University of Southampton. “In contrast, the incredible densities in neutron stars allow superconductivity at close to a billion degrees Celsius.”

Chandra X-ray telescope

Artist's impression of NASA's Chandra X-ray space telescope.

Cooling down

The discoveries were made when the researchers used NASA’s Chandra X-ray space telescope to investigate a sudden temperature drop on one particular neutron star 11,000 light years from Earth.

Heinke says this neutron star, known as Cassiopeia A, offered the researchers a great opportunity.

“It’s only 330 years old,” said Heinke. “We’ve got ringside seats to studying the life cycle of a neutron star from its collapse to its present, cooling off state.”

The researchers determined that the neutron star’s surface temperature is dropping because its core recently transformed into a superfluid state and is venting off heat in the form of neutrinos … sub-atomic particles that flood through the universe.

Here on Earth our bodies are constantly bombarded by neutrinos from space, with 100 billion neutrinos passing harmlessly though our eyes every second.

They also found that the neutron star’s core is a superconductor … the highest temperature (millions of degrees) superconductor known.

This research helps us to better understand the life cycles of stars, as well as the behaviour of matter at incredibly high densities.

Adapted from information issued by University of Alberta and NASA. Image credits: X-ray, NASA / CXC / UNAM / Ioffe / D. Page, P. Shternin et al.; optical, NASA / STScI; illustration, NASA / CXC / M. Weiss.

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How Kleopatra gave birth to twins

  • Asteroid Kleopatra is a rubble pile shaped like a dog bone, 217km long
  • Found to have twin 8km-wide moons that orbit it
  • Moons have been named after queen Cleopatra’s twins

ASTRONOMERS STUDYING two mini-moons orbiting an asteroid called Kleopatra have confirmed that the dog bone-shaped asteroid is probably a pile of rocky rubble instead of a solid body.

The French and American team, which includes Franck Marchis (University of California, Berkeley) and Pascal Descamps (Institut de Mecanique Celeste et de Calculs des Ephemerides, Observatoire de Paris), report their findings in the journal Icarus.

Kleopatra was discovered in 1880. Observations made in 2000 showed it to have an unusual, elongated shape reminiscent of a dog bone.

Subsequent radar observations confirmed the shape, but Marchis and his colleagues wanted higher resolution images to determine whether the two lobes of the dog bone are touching or are two separate bodies, and also to calculate its density.

The video above is a rotation of a computer model produced from the radar data.

Using the Keck II telescope in Hawaii, in 2008 the astronomers obtained the best images yet and confirmed that the asteroid is a double-lobed body. They also discovered the two small moons.

Space rubble

The team charted the orbits of the moons (diameters 3 and 5 kilometres), from which they could calculate the mass of the asteroid. Given its size, shape and mass, the astronomers then calculated the asteroid’s density—3.6 grams per cubic centimetre. (As a comparison, Earth’s average density is 5.5 grams per cubic centimetre.)

If the bulk of the asteroid is made of iron—a common component with a density of about 5 grams per cubic centimetre—then it must be between 30 and 50 percent empty space, the team concludes.

“Our observations of the orbits of the two satellites of … Kleopatra imply that this large metallic asteroid is a rubble pile, which is a surprise,” said Marchis, who is also a planetary scientist at the SETI Institute. “Asteroids this big are supposed to be solid, not rubble piles.”

Asteroid Kleopatra and its two tiny moons

Asteroid Kleopatra (overexposed in the left-hand image) and its two tiny moons. The image on the right has been processed to reduce the glare and more easily show the moons, which are now called Alexhelios and Cleoselene.

Kleopatra, about 217 kilometres long, is one of several large asteroids recently found to be composed of rocky rubble held together by mutual gravitational attraction. Others are Sylvia (280 kilometres in diameter), Antiope (86km), Hermione (190km) and 22 Kalliope (166km). Each of these has one or more moons, or in the case of Hermione, is itself a double asteroid.

How to grow a planet

The proportion of large asteroids in the Solar System that are rubble piles is unknown. But the fact that, so far, all multiple asteroids are porous collections of gravitationally bound chunks could have implications for how planets form, Marchis said.

Astronomers think planets are built up by rocks and asteroids crashing into each other and merging, with the resulting bodies gradually growing bigger and bigger.

But collisions between two asteroids are just as likely to smash both bodies to pieces ars they are to coalesce into a single large one, potentially making planet formation a slow process.

Rubble pile asteroids, however, would merge more easily during a collision.

Asteroid Kleopatra

Radar image of dog bone-shaped Kleopatra. The asteroid is thought be made of rocky rubble held together under its own weak gravitational field.

“If a large proportion of asteroids in the early Solar System were rubble-pile, then the formation of the cores of planets would be much faster,” Marchis said.

The twins leave home

Kleopatra probably coalesced from the remains of a rocky, metallic asteroid smashed to smithereens after a collision with another asteroid, which could have occurred any time since the origin of the Solar System 4.5 billion years ago.

Based on a theory of “binary asteroid” formation, the rubble pile would have been set spinning faster by another, oblique impact 100 million years ago. The spinning asteroid would have slowly elongated and eventually split off the most distant of its moons.

The inner moon was likely shed more recently, perhaps 10 million years ago.

The International Astronomical Union’s Committee on Small Body Nomenclature has accepted the proposal of Marchis and his collaborators to name the moons after Cleopatra’s twin children—Cleopatra Selene II and Alexander Helios.

The outermost moon has been named Alexhelios and the innermost moon Cleoselene. In Greek mythology, Helios and Selene represented the Sun and Moon, respectively.

Adapted from information issued by the University of California, Berkeley / NSSDC / NASA / Stephen Ostro et al. (JPL) / Arecibo Radio Telescope / NSF.

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